Method for transfer of information in a wireless cellular network

ABSTRACT

The present invention relates to a method for transmitting system information from a base station to a user equipment, the user equipment being a limited-bandwidth device, camping on the base station, wherein the system information are divided in a plurality of system information blocks, which are at least once transmitted during one broadcast channel modification period, the method comprising the step of—transmitting a first system information block the first system information block comprising at least—a broadcast channel change notification tag, and—a barring indication flag for limited-bandwidth devices, and wherein each other of the plurality of system information blocks is larger in size than the first system information block.

FIELD OF THE INVENTION

The present invention relates to a method for transmitting informationfrom a base station to a user equipment.

The invention also pertains to a base station using said method. Theinvention further relates to a user equipment configured to receiveinformation transmitted using said method.

BACKGROUND OF THE INVENTION

The cellular standards, in particular those supporting long termevolution (LTE) standard, are beginning to face the fact that differenttypes of user equipment are operating within the wireless networks. Aspecial interest is directed to so-called machine-type communicationdevices (MTC), which behave differently than mobile handsets.

As part of the standardization activities in Release 13 for such MTCdevices special channels and information blocks are foreseen.

One of the key elements is the definition of system information blocks(SIB). As part of that system information blocks dedicated for MTCdevices (M-SIBs) are suggested. System information is known to bedistributed in different system information blocks, which aretransmitted during one broadcast channel modification period.

Further MTC devices are separated in low complexity and low complexitydevices with Enhanced Coverage UEs. Low complexity is achieved byplacing in bandwidth reception capabilities lower demands than fornormal devices, i.e. those devices are only required to receive 1.4 MHzradio frequency bandwidth. The low complexity devices for enhancedcoverage are characterized that they are receiving or transmittinginformation in a repetitive manner and the receiver performing coherentaverage so that additional reception gain is achieved i.e. these arealso low complexity devices applying coverage enhancements techniques.These two categories of devices are defined in specification 3GPP TR36.888 V12.0.0, which content is incorporated here by reference.

Both of these types of devices address different use cases and henceplace different burdens on the SIB handling. It is in particularpreferable to address both types of devices with one common set ofM-SIBs.

The enhanced coverage devices typically considered as meters arestatic/semi-static and gain their enhanced coverage by repetitivereading of the related information. This is also applicable for the SIBsitself. The number of repetitions for enhanced coverage may be veryhigh, which leads to high latencies for receiving of all systeminformation in an UE. Times of 10.24 s are assumed to be acceptable forthese devices.

On the other hand generally SIB1 needs to be read in order to know if inat least one of the other system information blocks a change hashappened, which is indicated by the so-called BCCH value tag. Forenhanced coverage devices it is by now a challenge to successfullydecode the SIB1 during one broadcast channel modification period.

However, it is not only the latency but also the corresponding readingtime and consequently the battery consumption which causes aninappropriate operation of such devices. In particular repetitivereading during operation for e.g. acquiring the BCCH value tag or eventhe entire SIB structure leads to additional power consumption. This isin particular true in case of SIB reading operations of the UEs whichare in vain, due to the fact that the SIB1-reading could not be finishedduring the broadcast channel modification period.

It is therefore the goal of present invention to overcome the mentioneddisadvantages and to propose a solution for an improved transmission ofsystem information from a base station to a user equipment.

Further alternative and advantageous solutions would, accordingly, bedesirable in the art.

SUMMARY OF THE INVENTION

For this it is according to a first aspect of the invention suggested amethod for transmitting system information from a base station to a userequipment according to claim 1. It is further suggested according to asecond aspect of the invention a base station according to claim 7.Additionally it is suggested according to a third aspect of theinvention a user equipment according to claim 12.

According to the first aspect it is proposed a method for transmittingsystem information from a base station to a user equipment, the userequipment being a limited-bandwidth device, camping on the base station,wherein the system information are divided in a plurality of systeminformation blocks, which are at least once transmitted during onebroadcast channel modification period, the method comprising the step of

-   -   transmitting a first system information block, the first system        information block comprising at least    -   a broadcast channel change notification tag, and    -   a barring indication flag for limited-bandwidth devices,        and wherein each other of the plurality of system information        blocks is larger in size than the first system information        block.

The invention is based on the commonly known architecture of wirelesscellular networks according to technology standards like GSM, UMTS andLTE. As part of that, the base stations, resp. NodeB or eNodeB, transmitin a dedicated broadcast channel a defined collection of systeminformation to the user equipments which are operating with therespective base station. This operation relationship is called campingon a base station.

According to recent development it is foreseen to take into account theexistence of limited-bandwidth devices. These UEs form a special classof devices—in particular machine type communication devices—whichcomprise fewer resources for operating in the wireless cellular network,and are generally operating in a different manner than mobile handsets.

Furthermore limited-bandwidth devices might additionally be situated inplaces with only a comparably reduced receivable signaling power fromthe base station, where the UE is currently camping on. Suchlimited-bandwidth devices are called enhanced coverage devices, and theyare able to compensate the reduced signaling power by repeating to readthe signals, in order to get sufficient coverage gain.

The system information provided by the base station to the UEs is knownto be submitted in several blocks, the System Information Blocks (SIB).Typically the normal user equipment reads the first SIB—the SIB1. TheSIB1 comprises according to the present definition up to 20 fields ofinformation including the BCCH value tag. This BCCH value tag thatallows for the UE to derive whether the content of one of the SIBs haschanged. Based on that information the user equipment continues to readthe rest of the system information blocks transmitted by the basestation.

The system information blocks are completely transmitted during abroadcast channel modification period. When the SIB1 indicates with theBCCH value tag that no modification has happened, this status lasts forone broadcast channel modification period. The broadcast channelmodification period is typically configured by the wireless cellularnetwork in relationship to paging cycle and a predefined coefficientwhich takes values of the power of 2. Based on that the broadcastchannel modification period may take values between 0.64 and 40.96seconds, like it is shown in following table.

Paging cycle/ Coefficient 32 64 128 256 2 0.64 s 1.28 s 2.56 s 5.12 s 41.28 s 2.56 5.12 s 10.24 s 8 2.56 s 5.12 s 10.24 s 20.48 s 16 5.12 s10.24 s 20.48 s 40.96 s

The UE is able to derive the beginning and duration of the broadcastchannel modification period from network specific information like thepaging cycle and the received system frame number (SFN).

In order to support the additional type of user equipment it isdiscussed to introduce a separate set of system information forlimited-bandwidth devices. For those devices it is advantageous to usethe BCCH value tag in order to avoid unnecessary reading of SIBs.

In dependency of the size of the SIB1 and the broadcast channelmodification period it can happen for enhanced coverage devices, thatthe repetitive reading of the SIB1 does not finish during one broadcastchannel modification period. This is in particular due to twosituations:

a) the reading started not at the beginning of the broadcast channelmodification periodb) the reading time is larger than the broadcast channel modificationperiod.

The first situation means unnecessary reading efforts, hence powerconsumption invested in vain.

The second situation means, that when the SIB1 is read, the nextbroadcast channel modification period is reached, and therefore theinformation from the SIB1 may already be outdated. As it is known thatfor enhanced coverage devices that the reading of the current SIB1requires 500 repetitions and thus lasts up to 10 seconds, then the tableabove indicates that only for a minority of configurations the broadcastchannel modification period is long enough for reading a full SIB1 forenhanced coverage devices.

In order to solve that issue it is proposed to introduce to the set ofsystem information blocks for limited-bandwidth devices a small newSIB1, a so-called M-SIB1, which can be received by enhanced coveragedevices faster and would help to meet cost and power saving targets ofMTC devices much better. It is therefore envisaged to focus for theM-SIB1 on the absolute minimum content. Further it is preferable toaddress both types, the enhanced coverage devices and the commonlimited-bandwidth devices with the same type of M-SIBs.

Hence it is proposed that the M-SIB1 comprises a broadcast channelchange notification tag. This tag indicates to the UE that compared tothe last reading of the system information a change occurred in at leastone of the SIBs.

In one preferable embodiment the broadcast channel change notificationtag corresponds to the mentioned BCCH value tag.

In another preferably embodiment the broadcast channel changenotification tag simply comprises a binary value indicating if a changehas happened.

It is further proposed that the M-SIB1 comprises a barring indicationflag for limited-bandwidth devices. This flag indicates to the UE,whether reading is sensible at all for a MTC-device. Barring indicationsare important for network operators to push certain devices—in this caseMTC-devices—from operating with the currently active base station, inorder to maintain stability of the wireless cellular network. It isimportant that addressed UEs react without remarkable delay. Hence it isadvantageous to put the barring indication flag into the M-SIB1.

The M-SIB1 is the system information block of the plurality of systeminformation blocks with the smallest size. All other informationnecessary to be read are distributed over the rest of the systeminformation blocks. Having such a short M-SIB1 in advance of the furtherM-SIBs carrying the vast majority of information is beneficial for theUE in particular from power saving perspective as on the one hand systeminformation need to be read regularly and on the other hand—unlike tonormal UEs—SIB reading for enhanced coverage devices is power consuming.

Further this short M-SIB1 allows leaving the further relevant content ofthe M-SIBs in the SIBs and places where expected.

According to another preferred embodiment it is proposed a methodwherein the first system information block further comprises a nextbroadcast change occurrence notification tag.

With this embodiment the new M-SIB1 is enhanced by another element. Thenext broadcast change occurrence notification tag provides for thereceiving UE a prediction on when a change on the SIBs is expected.Hence the UE can estimate how many time and resources it can spend onreading the current system information blocks, or better wait until thenext change is supposed to occur. As the UE is able to judge how manyrepetitive receptions of the system information or a certain SIB itrequires to finish, with the information given in the suggested nextbroadcast change occurrence notification tag it is possible to decide ifthe UE continues reading or delays the reading until the next contentchange in the SIBs.

In particular the next broadcast change occurrence notification tagcomprises a number of broadcast channel modification periods. With thatthe UE knows the number of broadcast channel modification periods it canspend to read the system information. For this the duration of thebroadcast channel modification period is needed for the UE, which can bederived from the paging cycle and the SFNs.

Another simpler—and bitwise smaller—way would be to indicate the nextbroadcast change modification tag by a flag, which indicates if in thenext x broadcast change modification periods a content change isexpected, whereby the x is a defined constant or a value which isprovided by means of the system information.

In another preferred embodiment it is proposed a method wherein saidfirst system information block further comprises an indication relatingto at least one other of said plurality of system information blocks.

With this embodiment it is proposed to enhance the new M-SIB1 by anotherelement. According to this embodiment the M-SIB1 indicates in particularto the receiving UE where at least one other system information block issituated. This information is preferably provided by means of systemframe number (SFN) resp. an offset of SFN modulo paging period.

In particular this indication refers to a SIB resp. M-SIB where acontent change has happened compared to previous transmissions.

Alternatively the repetition or interleaving scheme of other SIBs isprovided to the UE, wherein the UE figures out how often and in whichorder the different SIBs are transmitted.

With these information the UE gets more detailed information and has thepossibility to only read the necessary SIBs in particular those where acontent change has happened. As for reading each SIB a couple ofrepetitions need to be read for limited-bandwidth devices, they canoptimize its efforts and power consumption.

Additionally in an advantageous embodiment it is proposed a methodwherein the minimum broadcast channel modification period forlimited-bandwidth devices is configured to last at least 10.24 seconds.

This embodiment basically suggests increasing the broadcast channelmodification period. This is in particular advantageous for enhancedcoverage devices, and makes sure that these devices are able to read allsystem information blocks during a broadcast channel modificationperiod.

The main reason for the current development in the opposite directionwas by now, that an MTC access barring would with the SIB-structure ofthe prior art lead to a very slow reaction of the UEs, which means upto >10 seconds. As the access barring of MTC devices is a securitymechanism of the wireless cellular networks in order to assure stabilityof the network, such times, which directly correlate with the broadcastchannel modification period, are not acceptable. Hence an increase ofthe broadcast channel modification period was not feasible.

Together with the proposed new M-SIB1, which include the barringindication flag, even enhanced coverage devices achieve to read anddecode the M-SIB1 much earlier than in the prior art. Hence an increaseof the broadcast channel modification period with the described resultsis possible without the negative impact on the wireless cellularnetworks.

This is in particular true, when the M-SIB1 is transmitted multipletimes during a broadcast channel modification period.

Preferably the M-SIB1 is the M-SIB which has the largest number ofrepetitions from all M-SIBs during a broadcast channel modificationperiod.

In a further advantageous embodiment it is proposed a method wherein thesystem information has associated a validity period, wherein thevalidity period for system information relating to limited-bandwidthdevices is longer than for system information relating tonon-limited-bandwidth devices.

With the validity period the user equipment receives an indication howlong the received system information, when no change occurs, is supposedto stay valid. Upon return from out of coverage a UE needs to judge ifthe previously read and stored system information messages are stillvalid. The validity period was in particular predefined by the standardsas a constant, in particular of 3 hours.

It is now proposed to introduce a second validity period forlimited-bandwidth devices. This second validity period is characterizedthat it is longer than the first validity period fornon-limited-bandwidth devices, in particular mobile handsets. A feasiblevalue for the second validity period would be 24 hours. Hence thelimited-bandwidth devices may—when it is operating in idle mode withoutany additional transmissions are receptions in between—wait this timeuntil it wakes up and read the M-SIB1. When a UE like a metering deviceis configured to send its data once per day or less than a day, with thefirst validity period it needed to read for each transmissions the fullSIBs. With the proposed enhancement of the validity period forlimited-bandwidth devices, for a good share of transmissions the systeminformation needs not to be carried out, but can be retrieved fromstored values. This is advantageous for limited-bandwidth devices interms of power saving.

It is in particular proposed that an indication on the maximum of atleast one of the validity periods is signaled as part of the systeminformation.

Compared to the known handling of validity periods it is proposed thatin particular for the second validity period an indication of themaximum value is indicated as part of the system information, hence inone of the M-SIBs.

Preferably this information is not supplied in the M-SIB1 in order notto increase the size of the M-SIB1.

The indication preferable comprises the number of hours, a certain classof validity periods, or any other indication relating to the envisagedvalidity period.

According to a second aspect of the invention it is proposed a basestation being part of a wireless cellular network, comprising at least atransmitter, the base station being configured to divide systeminformation for limited-bandwidth devices in a plurality of systeminformation blocks and transmitted at least once during one broadcastchannel modification period by means of the broadcast channel to alimited-bandwidth device, wherein the base station is further configuredto:

-   -   transmit a first system information block,        wherein the first system information block comprises at least:    -   a broadcast channel change notification tag, and    -   a barring indication flag for limited-bandwidth devices,        and wherein each other of the plurality of system information        blocks is larger in size than the first system information        block.

The base station is part of a wireless cellular network. The wirelesscellular network is in particular supporting long term evolution (LTE)standard, also known as a 4G-network. Typically the same wirelesscellular network comprises various radio access networks (RAN), like 2G,3G and 4G and its respective wireless technology standards (GSM, EDGE,UMTS, HSDPA etc.), where a base station is assigned to one RAN. Howeverat the same location, in particular in combined housings, preferablymore than one base station each supporting different RANs are supported.

Preferably the base station comprises at least a processing unit and atleast a memory unit, wherein computer programs are stored and executedin the processing unit, and carrying out the described operations of theproposed base station.

This aspect of the invention shares the advantages of the first aspect.

According to a third aspect of the invention it is suggested a userequipment configured for operating in camping relationship with a basestation of a wireless cellular network, the user equipment being alimited-bandwidth device, further configured to receive a first systeminformation block, comprising a part of system information being dividedinto a plurality of system information blocks, wherein the first systeminformation block comprises at least

-   -   a broadcast channel change notification tag, and    -   a barring indication flag for limited-bandwidth devices,        and wherein each other of the plurality of system information        blocks is larger in size than the first system information        block.

According to this aspect, a user equipment is foreseen that is operatingwith a base station according to the second aspect of the invention.

The user equipment is a device allowing wireless communication with thewireless cellular network and other user equipment operating in the sameor other wireless cellular networks or in a landline network, likeremote servers. The user equipment is a limited-bandwidth device, whichapplies in particular to machine type communication (MTC) devices, likemeters, vending machines etc. Typically a UE is composed of acontrolling appliance and a communication unit, which comprises allnecessary parts for wireless signaling from and to a base station. Itfurther comprises a processing unit and at least a memory unit storingsoftware programs for executing the operations. Further transmissionsfrom the base stations are stored in such memory units.

When a user equipment receives transmissions from a base station, thismeans that the transceiver of the communication unit gains the signalsfrom the base station with sufficient power and is able to decode thetransmitted messages.

This aspect of the invention shares the advantages of the first andsecond aspect.

It is further proposed according to an advantageous embodiment of thisaspect a user equipment configured to decide about receive of at leastone second system information block based on the information received inthe first system information block.

With this embodiment the user equipment, in particular an enhancedcoverage device, decides based on the retrieved data from the M-SIB1, ifanother M-SIB needs to be decoded. This is a reaction on the informationprovided with the M-SIB1.

In particular the broadcast channel change notification tag indicates ifa change in one of the M-SIBs has occurred. If the user equipment hasstored a complete set of system information from a previous readingeffort, and the validity period, in particular for limited-bandwidthdevices, has not expired, then the rest of the M-SIBs does not need tobe read and decoded, if the broadcast channel change notification tagindicates no change in the other M-SIBs. In particular when thebroadcast channel change notification tag consists of the BCCH valuetag, and the BCCH value tag equals the previously read and stored value,then the UE does not need to read the remaining M-SIBs of this broadcastchannel modification period. This is advantageous for power savingreasons for the UE.

As it is shown this invention advantageously solves the depicted problemand suggests a change that makes possible the operation of enhancedcoverage devices with the base stations in a manner complying with powerconsumption objectives.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the annexed drawings set forth in detailcertain illustrative aspects and are indicative of but a few of thevarious ways in which the principles of the embodiments may be employed.Characteristics and advantages of the present invention will appear whenreading the following description and annexed drawings of advantageousembodiments given as illustrative but not restrictive examples.

FIG. 1 represents schematically the transmissions of SIBs during abroadcast channel modification period according to the prior art;

FIG. 2 shows schematically the transmission of M-SIBs during a broadcastchannel modification period according to a preferred embodiment ofpresent invention.

FIG. 3 represents a first flow chart representing the process flow of afirst embodiment of the invention;

FIG. 4 represents a second flow chart representing the process flow of asecond embodiment of the invention.

FIG. 1 shows in a time diagram 1 the transmission of system informationblocks (SIBs) in a broadcast channel modification period 3 by one basestation. Here two successive broadcast channel modification period 3(n),3(n+1) are shown. They are delimited by the broadcast channelmodification period boundaries 4′, 4″, 4′″.

Each broadcast channel modification period lasts a defined number of mmilliseconds, depending of the preconfigured paging period p framesmultiplied with a coefficient c 2, 4, 8, 16, as well preconfigured bythe wireless cellular network, resp. the base station. With a frameduration of 10 ms the broadcast channel modification period can takevalues between 0.64 and 40.96 seconds.

The timepoint of the broadcast channel modification period boundary 4′,4″, 4′″ is calculated defined by system frame number (SFN) modulo m=0.

During one broadcast channel modification period 3 all the systeminformation blocks SIB1, SIBx are fully transmitted, typically thesystem information are distributed into 13 SIBs. The first SIB SIB1holds a couple of information for the user equipment which are campingon the respective base station. One of the information in the SIB1 isthe BCCH value tag VT. This is typically a number which is incrementedby one for each change of a SIBx resp. SIB1. When over two broadcastchannel modification periods the BCCH value tag VT stays constant, thisindicates to the receiving UEs that no change has happened on any of theSIBs.

Here it is indicated that during broadcast channel modification period3(n) the BCCH value tag VT′ in the SIB1 provides the value 42. In thenext broadcast channel modification period 3(n+1) the BCCH value tag VT″has the value 43. Hence, a change in the SIBs has happened betweenbroadcast channel modification period 3(n) and 3(n+1).

For an enhanced coverage device it takes some time to retrieve SIB1 dueto the necessary amount of repetitions in order to achieve sufficientcoverage gain. Arrow 2′ shows the time for an exemplary enhancedcoverage device for reading of the SIB1.

The UE starts reading amidst the broadcast channel modification period3(n), as it is indicate with arrow 2′. Due to the required duration thefull retrieval of SIB1 crosses boundary 4″, hence does not finish inbroadcast channel modification period 3(n). Due to that the UE needs torestart reading of SIB1, as the BCCH value tag VT might have changed inthe next broadcast channel modification period 3(n+1)—which is actuallythe case.

This shows that the first SIBx reading effort indicated with arrow 2′was fully in vain, instead again reading of the SIBx in the nextbroadcast channel modification period as indicated with arrow 2″ isnecessary.

Should the broadcast channel modification period 3(n) be even shorterthan 10.24 seconds, which is for the majority of network configurationsthe case, then an enhanced coverage device would never successfullyfinish reading the SIB1 during one broadcast channel modification period3, even less the SIBx.

FIG. 2 shows a similar time diagram 1 indicating a preferred embodimentof the invention. The first improvement is the enlarged broadcastchannel modification period 3(n), which allows longer time for enhancedcoverage devices to read the SIBs.

Further now SIBs dedicated for MTC devices are foreseen, that is herethe M-SIB1 and M-SIBx indicating the rest of the M-SIBs.

As it can be seen M-SIB1 is much shorter in size and hence in time to beread than it is known. It is preferably repeated more frequently duringone broadcast channel modification period than other M-SIBx.

It is indicated for this embodiment that the M-SIB1 consists of threefields: the MTC barring indicator BI, the system information value tagVT′ and the system information modification flag IM, which may indicatean upcoming change of system information in one of the next broadcastchannel modification periods 3(n+x).

The fields of M-SIB1 are summarized in following table:

SystemInformationBlockType1 field descriptions MTCBarringIndicatorbarred means the cell is barred for MTC device systemInfoValueTag Changeof any of the SIBs is indicated systemInfoModification Upcoming changeof information in next broadcast channel modification period

In the shown example for broadcast channel modification period 3(n) theM-SIB indicates that no MTC barring is activated, the current value tagis 42 and calculated from the current broadcast channel modificationperiod 3(n) the following 3(n+1) will provide a change in at least oneof the M-SIBx.

Arrow 2″′ indicates the duration for reading the M-SIB1 for an enhancedcoverage device. It can be seen that even start reading midst of thebroadcast channel modification period 3(n) is concluded successfullywithin the broadcast channel modification period 3(n).

By receiving the M-SIB1 the UE has all relevant information and for theshown example knows that MTC devices are currently not barred, andduring the next broadcast channel modification period 3(n+1) a change inat least one M-SIBx will happen, indicated through the specific M-SIB 5.

Would the system information modification tag IM show a higher value,then during broadcast channel modification period 3(n+1) the UE wouldnot have to receive and decode the M-SIBx at all. Due to the MTC barringindicator at least M-SIB1 needed to be read should the UE plan anyoperation with the base station, in particular a data transmission.

In this example the next M-SIB1′ during broadcast channel modificationperiod 3(n+1) now indicates modified values, which indicate that noMTC-barring is active (BI′=0), with value tag VT′ of value 43 that achange in one of the M-SIBs compared to the previous broadcast channelmodification period 3(n) has happened, and that no change is happeningin the next broadcast channel modification period (IM′=0).

Additionally some limited-bandwidth devices do not necessarily need theSIB repetitions, in particular UEs like cash-machines for credit-cardsor in parking lots, for which power consumption is a critical topic.Furthermore for those UEs the access time, i.e. the latency caused bythe SIB reading is very crucial as such UEs often are switched on andoff by the application and hence it is the initial access time whichaffects the user experience.

In many scenarios such machines are operated static or they are broughtto other locations i.e. credit-card machines in taxis or restaurants.Hence only a subset of these limited-bandwidth devices is configured toreliably access stored information. The rest needs to start again thewhole reading process. This requires from the SIB structure that it hasenough flexibility to allow for fast access. A value of 2.56 sec shouldbe feasible to acquire all information related to initial access fromthe M-SIBs. Such a value should lead to an overall system access timebeing in an order to operate also these devices in scenarios which areoften switched On and Off and cannot rely on stored information.

The decision and M-SIB scheduling should allow for bothlimited-bandwidth devices and enhanced coverage devices to be operatedin a manner that the proposed M-SIB reading times can be achieved.

FIG. 3 shows a flow chart for a UE operating with a base station ofreading the M-SIBs according to a preferred embodiment of the invention.

The process starts in step S10 with a UE camping on a base station. TheUE is a MTC device which is addressed by M-SIBs transmitted from a basestation according to a preferred embodiment of the invention.

In a first decision step S11 it is checked if the UE is an enhancedcoverage device. Enhanced coverage devices are in particular thosesituated in an area with only limited received signaling power.

The decision if it is an enhanced coverage device may be done in situdue to the limited received signaling power. Alternatively the enhancedcoverage characteristic is activated by a command, e.g. an AT command.

If the UE is not an enhanced coverage device, then the process branchesto step S12 and the UE simply reads the new M-SIB1 within one try.

Otherwise it is read the M-SIB1 in S13 and checked in step S14, ifsufficient coverage gain for M-SIB1 was received. If not it is jumpedback to S13, if so, the process jumps to step S15.

With a SIB1 according to the prior art, which has a size of ca. 1000Bits, it is expected that an enhanced coverage device needs to repeat upto 500 times the reading of the SIB1.

With the shorter M-SIB1 according to the invention, this amount ofcycles is reduced in particular proportionally to the reduction of size.This is particular means that during the operation steps from step S13to S15 most likely not broadcast channel modification period boundaryappears.

When the M-SIB1 is read—if by an enhanced coverage device or not—in thenext step S15 the received M-SIB1 is analyzed by the UE, that is theinformation fields are read out. In this embodiment it is then focusedin step S16 that the M-SIB1 indicates changes in the M-SIBx of thisbroadcast channel modification period. This is in particular done byanalyzing the broadcast channel change notification tag. In case thebroadcast channel change notification tag comprises the BCCH value tag,then the UE needs to compare the determined value tag with a storedvalue tag of a previously read M-SIB1 within a previous broadcastchannel modification period.

If the value tag is incremented compared to the previous value, then thestored value is in particular replaced by the new value.

Further the UE thus detects that at least one of the M-SIBx during thisbroadcast channel modification period has changed. Hence the UEcontinues reading the M-SIBx in step S17. Of course, depending on thefact if the UE is an enhanced coverage device or not, the step S17requires repetitions as well.

In case the M-SIB1 comprises an indication relating to one particularM-SIBx, which is determined by the UE during the analysis step S15, thenthe UE is able in step S17 to read the data from a dedicated M-SIBx,which reduces the amount of reading cycles, hence also the amount ofrequired energy for reading the changed M-SIBx.

In effect the content of the M-SIB1 is used by the UE to decide aboutreading further M-SIBx or not.

FIG. 4 shows in a flow chart another embodiment of present invention. Itstarts again in step S20 with a UE camping on a base station. Then it isread the M-SIB1 in step S21. For simplification purposes the distinctionbetween enhanced coverage devices and regular limited-bandwidth devicesis omitted in this flow chart. However the steps shown in FIG. 3 areapplicable to this process flow as well, which applies to later steps ofreading an M-SIB as well. After the M-SIB1 is read, it is analyzed instep S22 that means the comprised fields are read out. If that analysisshows in the barring indication flag BI that MTC devices are barred fromoperating with this base station, then in step S23 it is branched tostep S24. This results in a termination of the operation of the UE withthe base station. It is preferable to first check the barring indicationbefore any other analysis is carried out by the UE.

If the barring indicator is not set, then the process branched to stepsS25. Here it is checked if the M-SIB1 indicates an upcoming change of anM-SIBx by means of the next broadcast change occurrence notificationtag.

If no such change is indicated then the UE can assume, that in the nextbroadcast channel modification period no other information aretransmitted than in the current broadcast channel modification periodand/or in a previous broadcast channel modification period and where theM-SIBx values are stored in a memory unit within the UE.

For reverting to the M-SIBx values stored in the memory unit it ispreferably considered the validity period of the system information. Inparticular in case of a set of validity periods related to the M-SIBs,which means a validity period for limited-bandwidth devices and enhancedcoverage devices, the respective validity period for the M-SIBs is to betaken into account. This is additionally true when the UE wasdeactivated and returns into operation. When the M-SIBx then indicatesstill the same BCCH value tag, the UE does not need to read the M-SIBxagain, as long as the validity period is not expired. As for MTC devicessuch deactivation phases might last hours to days, a longer validityperiod than for mobile handset is advantageous and saves power resourcesat the MTC device.

Here the subsequent steps are depending on other system informationfields in the M-SIB1, in particular the broadcast channel changenotification tag. Hence the process flow shown in FIG. 3 is applicablehere as well.

However should the next broadcast change occurrence notification tagindicate that in one of the following broadcast channel modificationperiods a content change in at least one of the M-SIBx is expected, thenthe process follows in step S26.

In that case the reading of the M-SIBx of the current broadcast channelmodification period is preferably omitted, at it is expected that theseinformation will be outdated in the next broadcast channel modificationperiod.

Hence it is waited in step S27 until the next broadcast channelmodification period starts.

Although the UE knows, that the M-SIBx will provide at least one contentchange, it is nevertheless necessary to read first the M-SIB1 of the newbroadcast channel modification period in step S28.

It is expected that the broadcast channel change notification tag willprovide an incremented BCCH value tag. Nevertheless still a barringindication flag might require the UE to terminate the operation withthis base station.

Additionally an indication relating to the changed M-SIBx is preferablycomprised in the M-SIB1 and allows for the UE to directly read only thechanged M-SIBx.

All the necessary checks and exceptions are indicated with theinterrupted arrow between step S28 and S29. Hence, in step S29 all or atleast the changed M-SIBx of this broadcast channel modification periodis read.

It can easily be seen that the problem for the envisaged UEs with theknown structure of SIBs and broadcast channel modification periods willbe solved with the invention. This allows for the enhanced coveragedevices an operation with an optimization in terms of power consumption,reliability and response times.

In the above detailed description, reference is made to the accompanyingdrawings that show, by way of illustration, specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. It is to be understood that the various embodiments of theinvention, although different, are not necessarily mutually exclusive.For example, a particular feature, structure, or characteristicdescribed herein in connection with one embodiment may be implementedwithin other embodiments without departing from the scope of theinvention. In addition, it is to be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the scope of the invention. The abovedetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims, appropriately interpreted, along with the full range ofequivalents to which the claims are entitled.

1. Method for transmitting system information from a base station to auser equipment, the user equipment being a limited-bandwidth device,camping on the base station, wherein the system information are dividedin a plurality of system information blocks, which are at least oncetransmitted during one broadcast channel modification period, wherein atleast one system information block further comprises a broadcast channelchange notification tag indicating if a change on the system informationhas happened, and an element indicating in which system informationblock a content change has happened.
 2. Method according to claim 1,comprising the step of transmitting a first system information block thefirst system information block comprising at least a barring indicationflag for limited-bandwidth devices, and wherein each other of theplurality of system information blocks is larger in size than the firstsystem information block.
 3. Method according to claim 2 wherein thefirst system information block further comprises a next broadcast changeoccurrence notification tag.
 4. Method according to claim 2, whereinsaid first system information block further comprises an indicationrelating to at least one other of said plurality of system informationblocks.
 5. Method according to claim 1, wherein the system informationfurther has associated a validity period, wherein the validity periodfor system information relating to limited-bandwidth devices is longerthan for system information relating to non-limited-bandwidth devices.6. Method according to claim 5, wherein an indication on the maximum ofat least one of the validity periods is signaled as part of the systeminformation.
 7. Base station being part of a wireless cellular networkcomprising at least a transmitter, the base station being configured todivide system information for limited-bandwidth devices in a pluralityof system information blocks and transmitted at least once during onebroadcast channel modification period by means of the broadcast channelto a limited-bandwidth device, wherein the base station is furtherconfigured to: transmit a first system information block, wherein thefirst system information block comprises at least a broadcast channelchange notification tag, indicating if a change on the systeminformation has happened, and an element indicating in which systeminformation block a content change has happened.
 8. Base stationaccording to claim 7 wherein the first system information block furthercomprises a barring indication flag for limited-bandwidth devices, andwherein each other of the plurality of system information blocks islarger in size than the first system information block.
 9. Base stationaccording to claim 7, wherein the first system information block furthercomprises a next broadcast change occurrence notification tag.
 10. Basestation according to claim 7, wherein said first system informationblock further comprises an indication relating to at least one other ofsaid plurality of system information blocks.
 11. Base station accordingto claim 7, wherein the base station is further configured to associatea validity period to the system information for limited-bandwidthdevices, wherein the validity period of system information forlimited-bandwidth devices is longer than for system information relatingto non-limited-bandwidth devices.
 12. Base station according to claim11, further configured to transmit as part of the system information anindication on the maximum of at least one of the validity periods. 13.User equipment configured for operating in camping relationship with abase station of a wireless cellular network, the user equipment being alimited-bandwidth device, further configured to receive a first systeminformation block, comprising a part of system information being dividedinto a plurality of system information blocks, wherein the first systeminformation block further comprises at least a broadcast channel changenotification tag, indicating if a change on the system information hashappened, and an element indicating in which system information block acontent change has happened.
 14. User equipment according to claim 13,wherein the first system information block further comprises a barringindication flag for limited-bandwidth devices, and wherein each other ofthe plurality of system information blocks is larger in size than thefirst system information block.
 15. User equipment according to claim13, wherein the first system information block further comprises a nextbroadcast change occurrence notification tag.
 16. User equipmentaccording to claim 13, wherein said first system information blockfurther comprises an indication relating to at least one other of saidplurality of system information blocks.